Geological Origins of Cardiff
Long before man set foot on the earth, mighty forces of nature
shaped the landscape which he would inherit and exploit. Over 500 million years
ago, the region we know as South Glamorgan was
covered by a warm, shallow sea. About that time volcanic eruptions began a
process which was to deposit the oldest rocks of Glamorgan in the Penylan
district of Cardiff. Though more than 400 million years old, these stones
appear relatively young when we remember that their age is a mere tenth of the
most ancient rocks known to man.
Since those first volcanic
disturbances, the action and interaction of sun, wind, rain, frost and ice have
been at work to create the natural environment of South
Wales. First came a lengthy period when vast accumulations of sand
from distant deserts, aided by a warm wet climate, created the red sandstone
which is a feature of the Brecon Beacons to this day.
and a tropical sea covered the area. Evidence of a clear coral lagoon has been
discovered at Barry Island where the sediment
provided a fertile environment for molluscs, corals and sea lilies. Eventually
this silt came to the surface as carboniferous limestone, a rock which is still
visible in the gorge at Taffs Well, on the islands of Flatholm and Steepholm,
and in the Vale of Glamorgan. For many years this limestone has been quarried
at Wenvoe and much of the material used in the construction of Barry Docks came
About 300 million
years ago the sea level fell away to produce a marshy plain, criss-crossed by
innumerable streams. The climate was humid and tropical, turning the plain into
a swampy jungle. As the lush, rotting
vegetation was buried under a layer of mud and sand, rich seams of coal
were formed. In the Vale of Glamorgan they eventually became eroded and
disappeared, but to the north these seams evolved as the South
Wales coalfield. Thus was created the mineral wealth which brought
prosperity to Victorian Cardiff and the mining valleys.
lengthy period of desert-like conditions followed, as sand and dust were blown
together to shape Triassic sandstones and marls. They can be seen along the
coastline from Penarth to Barry, and the attractive Radyr stone is also a
legacy of this period. The stones in the Gorsedd circle at Cathays Park are natural examples of Triassic sandstone, and much of the material used to
build Victorian Cardiff came from this source.
Triassic era, dinosaurs roamed the earth. In 1974 the footprints of one of
these monsters was found near Porthcawl and in 1990 more extensive impressions
were discovered near the Atlantic Trading Estate at Barry. Preserved under a
mixture of mud and sand, some of these footprints are thought to have been made
by the Coelophysis. This was a strange beast, approximately four feet high and
measuring about eight feet from head to tail. In appearance it resembled a
kangaroo, walking on its hind legs to leave a distinctive image of its three
toes in soft mud. These fossils from the age of the dinosaurs can be seen in
the National Museum of Wales.
Once more the sea
flooded the land, bringing in its wake the shale and Liassic limestone so
characteristic of the Vale of Glamorgan. In time this limestone would be used
to build Cardiff Castle, St. John's Church,
Llandaff Cathedral and many churches in the Vale itself. The limestone also
produced a light but fertile, stony soil which could be cultivated with the
primitive tools of the earliest farmers.
One more great
geological transformation was to occur. The Ice Age began about a million years
ago and finally terminated a mere 10,000 years from our own lifetime. Massive
glaciers covered most of South and Central Wales.
As they melted in the fullness of time, so the sea level rose and the future
English and Bristol Channels at last made their appearance. The melting
glaciers left a fine debris which became the basis of our clay and gravel
soils. Much of Cardiff is built on the deposits of this final stage of creation.
Prehistory galleries at The National Museum of Wales
North F.J. “The Geological History of the Vale”, in “The
Garden of Wales”, ed.
Stewart Williams (Barry